1. Field of the Invention
This invention relates to a process for heat treating highly hygroscopic coal having much inherent moisture with hot gas to make it less hygroscopic.
2. Description of the Prior Art
Of coals, those which have attained high degrees of coalification contain little inherent moisture and, in general, removal of surface moisture permits them to dry for use with economy. Coals with low degrees of coalification, on the other hand, have such large inherent moisture that mere removal of surface moisture is not effective enough for the drying purpose.
To achieve the end with coal of a low coalification degree, it has generally been the practice to dry the coal at elevated temperatures, high enough to drive out the inherent moisture.
Drying the less-coalified coal in this way, however, is not helpful in lowering its hygroscopicity, and the dried coal is still highly hygroscopic. During subsequent transportation and storage, the coal takes up moisture from the air, resuming the original state minus the surface moisture (the state being hereinafter called that of equilibrium moisture). This adds to the transportation and storage cost and, moreover, the commercial value of the coal is impaired by a decrease in its calorific value.
The present invention has now been perfected in view of the foregoing, and it is a primary object of the invention to provide a process for heat treating coal with a low degree of coalification to remove its moisture, convert it to less hygroscopic and more economically valuable coal with an increased calorific value per unit weight.